Commit 35ebf65e authored by David S. Miller's avatar David S. Miller
Browse files

ipv4: Create and use fib_compute_spec_dst() helper. 



The specific destination is the host we direct unicast replies to.
Usually this is the original packet source address, but if we are
responding to a multicast or broadcast packet we have to use something
different.

Specifically we must use the source address we would use if we were to
send a packet to the unicast source of the original packet.

The routing cache precomputes this value, but we want to remove that
precomputation because it creates a hard dependency on the expensive
rpfilter source address validation which we'd like to make cheaper.

There are only three places where this matters:

1) ICMP replies.

2) pktinfo CMSG

3) IP options

Now there will be no real users of rt->rt_spec_dst and we can simply
remove it altogether.

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 70e73416

include/net/ip_fib.h

+1 −0
Original line number Diff line number Diff line
@@ -230,6 +230,7 @@ extern struct fib_table *fib_get_table(struct net *net, u32 id); 
/* Exported by fib_frontend.c */

extern const struct nla_policy rtm_ipv4_policy[];

extern void		ip_fib_init(void);

extern __be32 fib_compute_spec_dst(struct sk_buff *skb);

extern int fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,

			       u8 tos, int oif, struct net_device *dev,

			       __be32 *spec_dst, u32 *itag);

net/ipv4/fib_frontend.c

+29 −0
Original line number Diff line number Diff line
@@ -180,6 +180,35 @@ unsigned int inet_dev_addr_type(struct net *net, const struct net_device *dev, 
}

EXPORT_SYMBOL(inet_dev_addr_type);



__be32 fib_compute_spec_dst(struct sk_buff *skb)

{

	struct net_device *dev = skb->dev;

	struct in_device *in_dev;

	struct fib_result res;

	struct flowi4 fl4;

	struct net *net;



	if (skb->pkt_type != PACKET_BROADCAST &&

	    skb->pkt_type != PACKET_MULTICAST)

		return ip_hdr(skb)->daddr;



	in_dev = __in_dev_get_rcu(dev);

	BUG_ON(!in_dev);

	fl4.flowi4_oif = 0;

	fl4.flowi4_iif = 0;

	fl4.daddr = ip_hdr(skb)->saddr;

	fl4.saddr = ip_hdr(skb)->daddr;

	fl4.flowi4_tos = RT_TOS(ip_hdr(skb)->tos);

	fl4.flowi4_scope = RT_SCOPE_UNIVERSE;

	fl4.flowi4_mark = IN_DEV_SRC_VMARK(in_dev) ? skb->mark : 0;



	net = dev_net(dev);

	if (!fib_lookup(net, &fl4, &res))

		return FIB_RES_PREFSRC(net, res);

	else

		return inet_select_addr(dev, 0, RT_SCOPE_UNIVERSE);

}



/* Given (packet source, input interface) and optional (dst, oif, tos):

 * - (main) check, that source is valid i.e. not broadcast or our local

 *   address.

net/ipv4/icmp.c

+4 −2
Original line number Diff line number Diff line
@@ -95,6 +95,7 @@ 
#include <net/checksum.h>

#include <net/xfrm.h>

#include <net/inet_common.h>

#include <net/ip_fib.h>



/*

 *	Build xmit assembly blocks
@@ -333,7 +334,7 @@ static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb) 
	struct flowi4 fl4;

	struct sock *sk;

	struct inet_sock *inet;

	__be32 daddr;

	__be32 daddr, saddr;



	if (ip_options_echo(&icmp_param->replyopts.opt.opt, skb))

		return;
@@ -347,6 +348,7 @@ static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb) 


	inet->tos = ip_hdr(skb)->tos;

	daddr = ipc.addr = ip_hdr(skb)->saddr;

	saddr = fib_compute_spec_dst(skb);

	ipc.opt = NULL;

	ipc.tx_flags = 0;

	if (icmp_param->replyopts.opt.opt.optlen) {
@@ -356,7 +358,7 @@ static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb) 
	}

	memset(&fl4, 0, sizeof(fl4));

	fl4.daddr = daddr;

	fl4.saddr = rt->rt_spec_dst;

	fl4.saddr = saddr;

	fl4.flowi4_tos = RT_TOS(ip_hdr(skb)->tos);

	fl4.flowi4_proto = IPPROTO_ICMP;

	security_skb_classify_flow(skb, flowi4_to_flowi(&fl4));

net/ipv4/ip_options.c

+11 −11
Original line number Diff line number Diff line
@@ -27,6 +27,7 @@ 
#include <net/icmp.h>

#include <net/route.h>

#include <net/cipso_ipv4.h>

#include <net/ip_fib.h>



/*

 * Write options to IP header, record destination address to
@@ -104,7 +105,7 @@ int ip_options_echo(struct ip_options *dopt, struct sk_buff *skb) 
	sptr = skb_network_header(skb);

	dptr = dopt->__data;



	daddr = skb_rtable(skb)->rt_spec_dst;

	daddr = fib_compute_spec_dst(skb);



	if (sopt->rr) {

		optlen  = sptr[sopt->rr+1];
@@ -250,15 +251,14 @@ void ip_options_fragment(struct sk_buff *skb) 
int ip_options_compile(struct net *net,

		       struct ip_options *opt, struct sk_buff *skb)

{

	int l;

	unsigned char *iph;

	unsigned char *optptr;

	int optlen;

	__be32 spec_dst = (__force __be32) 0;

	unsigned char *pp_ptr = NULL;

	struct rtable *rt = NULL;

	unsigned char *optptr;

	unsigned char *iph;

	int optlen, l;



	if (skb != NULL) {

		rt = skb_rtable(skb);

		spec_dst = fib_compute_spec_dst(skb);

		optptr = (unsigned char *)&(ip_hdr(skb)[1]);

	} else

		optptr = opt->__data;
@@ -330,8 +330,8 @@ int ip_options_compile(struct net *net, 
					pp_ptr = optptr + 2;

					goto error;

				}

				if (rt) {

					memcpy(&optptr[optptr[2]-1], &rt->rt_spec_dst, 4);

				if (skb) {

					memcpy(&optptr[optptr[2]-1], &spec_dst, 4);

					opt->is_changed = 1;

				}

				optptr[2] += 4;
@@ -372,8 +372,8 @@ int ip_options_compile(struct net *net, 
						goto error;

					}

					opt->ts = optptr - iph;

					if (rt)  {

						memcpy(&optptr[optptr[2]-1], &rt->rt_spec_dst, 4);

					if (skb)  {

						memcpy(&optptr[optptr[2]-1], &spec_dst, 4);

						timeptr = &optptr[optptr[2]+3];

					}

					opt->ts_needaddr = 1;

net/ipv4/ip_sockglue.c

+4 −3
Original line number Diff line number Diff line
@@ -40,6 +40,7 @@ 
#if IS_ENABLED(CONFIG_IPV6)

#include <net/transp_v6.h>

#endif

#include <net/ip_fib.h>



#include <linux/errqueue.h>

#include <asm/uaccess.h>
@@ -1019,8 +1020,8 @@ e_inval: 
 * @sk: socket

 * @skb: buffer

 *

 * To support IP_CMSG_PKTINFO option, we store rt_iif and rt_spec_dst

 * in skb->cb[] before dst drop.

 * To support IP_CMSG_PKTINFO option, we store rt_iif and specific

 * destination in skb->cb[] before dst drop.

 * This way, receiver doesnt make cache line misses to read rtable.

 */

void ipv4_pktinfo_prepare(struct sk_buff *skb)
@@ -1030,7 +1031,7 @@ void ipv4_pktinfo_prepare(struct sk_buff *skb) 


	if (rt) {

		pktinfo->ipi_ifindex = rt->rt_iif;

		pktinfo->ipi_spec_dst.s_addr = rt->rt_spec_dst;

		pktinfo->ipi_spec_dst.s_addr = fib_compute_spec_dst(skb);

	} else {

		pktinfo->ipi_ifindex = 0;

		pktinfo->ipi_spec_dst.s_addr = 0;

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